Battery what is the battery size

The Casio Forester FT500WVB watch has an EL (Electroluminescent) backlight and requires one silver oxide button battery. The SR621W battery (also known as type 363) is recommended by the instruction manual for the watch. Note the suffix "W" means this battery is a high drain type which is suitable for powering a watch mechanism and the EL light as well for 2 to 3 years, depending on use of the light. "SW" suffix batteries are low drain and are intended only to power a watch mechanism, and not a light. Note also the "SR" prefix indicates the battery is silver oxide and not lithium. The SR type batteries do not use mercury and are therefore safer to dispose of when they are discharged. I have found the type SR626W (also known as type 377) battery is also suitable for the FT500WVB watch and it has more stored power and should therefore last longer.

Last, the Casio Forrester FT500WC looks exactly like the FT500WVB, but it is a different watch internally. The FT500WC has an LED light and requires two batteries- the SR920SW low drain silver oxide battery which powers the watch mechanism and the CR1616 lithium battery which powers the LED. The LED is brighter than an EL light and stays on longer than the EL light when activated. But the LED has a bright dot light source that some might find annoying.